1. Field
The invention relates to motor servo systems and particularly to a servo drive system which utilizes a Hall or optical element as multiplier means to drive as well as servo control a motor.
2. Prior Art
Typical prior art servo systems for controlling motor speed are those commutated by conventional brushes, by brushless means, by Hall elements, etc. Motors commutated by conventional brushes generate torque and velocity perturbations which cannot be tolerated in high precision motor drive systems, have serious top speed limitations, generate unacceptable electrical interference, etc.
Brushless motors in general have been of the bipolar type, wherein those with four coils and two poles, or with two coils with intermediate taps, have large variations in torque produced within one revolution of 360.degree.. At slow speeds such as 1000 rpm, intense vibrations and variations in rotational speed are generated.
Motors employing Hall elements provide multipolar brushless commutations while supplying switching signals to a digital commutator. This drive system generates undesirable torque and velocity perturbations in the motor which also are unacceptable in high precision systems. That is, the motor is driven with square wave drive signals which produce discrete torque perturbations during motor rotation, i.e., the torque generated has discrete discontinuities which appear as very small velocity perturbations.
The above prior art drive systems in general require additional motor drive amplifiers which adds complexity to the motor drive, particularly in a bidirectional drive system.